The present study explored the anaerobic co-digestion (AcD) of seaweed Gracilaria vermiculophylla with fat, oil, and grease (FOG) at 75, 50, and 25 % w/w of volatile solids (VS). Mono-digestion of FOG and SW led to a methane production of 133 and 109 mL/(g.d) with 40 days lag-phase, lower than 235 mL/(g.d) of AcD at FOG-50:SW-50 with reduced lag-phase of 20 days. The palmitic and oleic acid reduction was 95 % in the reactors FOG-50:SW-50, followed by FOG-25:SW-75, which was 84 %, as compared to FOG mono-digestion (47 %). Relative abundance of Firmicutes, Chloroflexi, and Bacteroidetes were enriched during AcD. The relative abundance of Methanosaeta was enhanced (40-90 %) in FOG-50:SW-50 compared with FOG-100:SW-0 as the reduction in Methanosaeta was replaced by Methanoculleus (30 %) and RuMen-M2 (10 %). The present study offers essential perspectives for the AcD of FOG with SW, showcasing the benefits of SW as a co-substrate for improved methane recovery from FOG.